The present invention relates to systems for detecting the presence of concealed materials, and in particular to such a system which uses gamma-ray induced X-ray fluorescence and a scanning spectroscope to detect the presence of specific material in concealed locations such as luggage or other containers.
The use of X-rays to detect or examine the contents of luggage, packages and the like is well known. Such systems, however, are only capable of detecting the presence of high density elements such as steel, lead and the like. Many materials cannot be detected with current X-ray systems.
It has been proposed to use fast neutron activation of concealed materials for the detection of low density elements. It is known that some elements like nitrogen produce an isotope that emits a beta decay positron which in turn reacts with electron producing a 511 keV annihilation gamma ray. However, the resulting nucleus that produces these positrons has a half life of about ten minutes. This creates problems since even after one hour the radioactivity of the sample has dropped by only a factor of 5. Further, even using high-flux fast neutron sources, the resultant count rate of the emitted gamma rays is sufficient only to determine the presence of a particular element in a sample and not to get is spatial distribution. To produce a spatial distribution picture requires a long period of time, typically, in excess of one hour. Such systems require the use of complex technology and are expensive.
Therefore, there has been a need for a system that detects low density materials concealed in articles such as luggage and containers and the like, which is capable of producing a real-time detection of such materials and is capable of providing a spatial distribution or picture of these materials.